Transmitter



v' May 29, 1923. 1,456,513

J. P. MINTON TRANSMITTER Filed Sent. 5, 1919 mvenfw s John MM 70mlPatenteol May 2%, 1%23.

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TRANSMITTER.

Application filed September 5, 1919. Serial No. 321,914.

To all whom it may concern:

Be it known that T, JoHN lP. MINTON, a

citizen of the United States,' residing at' concise, and exactdescription.

This invention relates to transmitters and particularly to a type oftransmitter especially adapted for use in places where such apparatus issubjected to severe extraneous noises or vibrations set up by the rushof air.

In various places there is a demand for a transmitter which will operateefliciently in picking up the feeble voice waves and yet will notrespond appreciably to extraneous sounds or to violent disturbances ofthe air. Such a transmitter is a necessity in connection with theintercommunicating sets used on airplanes for communication between thepilot and the'observer, and also for wireless communication from theplane to a ground station or to another airplane. The dieturbances setup by the exhaust of the en gine and the rush of air through the-guywires is so violent as to make audible speech impossible between thepilot and the observer and telephone apparatus is provided as thenecessary means of communication. The transmitters employed under thiscondition must operate satisfactorily on the faint sound waves when onetalks into the transmitter and yet not be appreciably affected by theextraneous noises. Again, in

connection with telephone apparatus used for fire control, either onbattle ships or on land fortifications, it is necessary that thetransmitter easily and intelligibly transmit speech even thoughsubjected to the violent concussion due to the discharge of nearby ofthe air occurring nearby.

A still further object of the invention is to provide a transmitter ofthe type in question which will be cheap to manufacture,

will not have any delicate parts which will require ex ert attention andone in which the operating parts are protected from inury.

To accomplish these objects and in accordance with a feature of thisinvention, thereais provided a transmitter in which means 1s providedfor preventing vibrations outside of the range of useful voicefrequencies from affecting the diaphragm and a resonant chamberisprovided for magnifying the effect of vibrations coming within therange of useful voice frequencies.

This and other features of the invention will be more clearly understoodby reference to the accompanying drawing, in which Fig. 1 is a sectionalview of a transmitter embodying this invention, and Fig. 2 is a view inperspective of the various parts of the transmitter placed in positionfor assembl Referring now to the drawing, there is disclosed acup-shaped casing 5 within which the .transmitter button is mounted. Thetransmitter face plate comprising an outer member 6 and an inner member7 is secured to the cup-shaped member 5 by means of screws which passthrough the countersunk holes 8- 8 in member 6 and the perforations 9-9in member 7, and thence {into shouldered bushings 1010 which 'arerigidly secured to the flanged portion of the aluminum casing 5. Thebushings 10-10, which are preferably of nickelsilver, are providedbecause of the difliculty of forming threads in the'aluminum'casing andare of suflicient length to extend into suitable openings 1111 in thespacer ring 12 and thereby prevent this ring from rotating. The ring 12is provided with since for the mounting of the damping spring 14 whichis insulated from the casing chamber in front of the diaphragm and ispreferably approximately twelve-thousandths of an inch. The centralportion of member 7 is provided with a number of perforations 4-4 whichare approximately forty-thousandths of an inch in diameter and lead fromthe inner resonating chamber next to the diaphragm to an outerresonating chamber 20 which is formed within the hub portion 21 ontheouter side of member 7. The face plate member 6 is provided with acounterbored-portion adapted to fit over the hub portion 21 of member 7and a ring 22 preferably ofoiled linen is provided as shown in order toinsure a tight chamber.

The member 6 is provided at its center with.

in lace by means of a plate 25 of hard rub er or other suitablenon-metallic material and the button-head screws 26-2 6- pass throughthe perforations 27-27 in plate 25 and engage the threads of corresonding perforations 2828 inmember 6. entrally located at the rear of thecasin 5 is the shouldered bridge center 30, whicli is held in place bythe lock nut 31 and is insulated from the casing by means of theinsulating washers 3232 and the insulating bushing 33. Located betweenthe shouldered portion ofthe bridge center 30 and the outer insulatingwasher 32 is a metal plate 29 having an extended portion which isprovided with a terminal screw 42. The bridge center 30 is bored out toreceive the shank 34 of a standard type of transmitter button comprisinga cup member 35 in which are located the front electrode 36 and the backelectrode 37, the remainder of the space being practically filled withgranular carbon which is held in place by means of the mica annulus 38and the retaining nut 39. The front stud 40, which is in directelectrical contact with the front electrode 36, is held firmly againstthe'center of the diaphragm 18 by .the tension of the damping sprin 14.After the transmitter has been assem led and the button properly locatedby the tension of spring 14, the button is locked in position bytightening screw 41 which is threaded into the bridge center 30 andbears against the shank 34 of the transmitter button. A metal plate 44is secured to the rear of casin 5- and insulated therefrom by means of ap ate 45 of hard rubber or other 'tive y large diameter and which may.allgnment with the perforations 23--23 in conductor 48 extends fromstud 46 to extension 49 of the damping spring 14, hence the screw 50which threads into the plate 44 serves as a terminal member for thefront electrode of the transmitter button. The other terminal screw 42engages the plate 29 which is in direct electrical contact with the backelectrode 37 but is insulated from the casing, hence in the transmitteras illustrated, the casing is not included in the electrical circuit.

Since in airplane service it often becomes necessary to use thetransmitter at very low temperatures, plate 25 which is preferably ofhard rubber or some other non-heat conducting material is provided forthe purpose of preventing the user from placing his lips in contact withan metal portion. This plate is provided at its center with a number oferforations 52 which are of com araplate member 6.

A transmitter of thetype described has been found in service to be verysatisfactory for use on airplanes, the construction being such as topermit the eflicient transmission of voice waves in spite of thedisturbances set up by the exhaust of the engine and the rush of wind.This is accomplished by the combination of the auxiliary resonatingchamber with the restricted openings on either side. The auxiliarychamber acts as a resonator for a band of frequencies within the limitsof useful speech frequencies (for example 300 to 1800 cycles) andamplifies, 1

or rather intensifies, by sympathetic vibrations of the air Within thechamber, the effect on the transmitter diaphragm of'the voice soundswhich are important. A large percentage of'the disturbing noise is of ahigh frequency nature, corresponding to the hissing noises produced bythe exhaust of the engine and the whistling. of the wind through thewires. The holes -2323, due to their small diameter and appreciablelength, act as a. filter-or shield to prevent such vibrations fromentering the resonating chamber 20. ,The natural frequency of thischamber is much lower than the frequency of the vibrations to beeliminated, hence the 120 chamber serves to further impede suchvibrations, since its impedance to sound transmission increases with thefrequency of the vibrations to be transmitted. Such vibratigns arefurther filtered out by means of the small holes 4-4 in plate 7 and arefurther impeded by the thm resonating chamber between the plate 7 andthe diaphragm 18. Vibrations of useful voice frequencies are somewhatimpeded by the small perfora- 139 'tions 23 but are amplified by meansof resonating chamber 20 which is so dimensioned as to be resonant atvibrations of voice frequency. The chamber between the plate 7 and thediaphragm 18 also acts as a resonating chamber and in addition providesa certain amount of air damping for the diaphragm 18. I

It will, therefore, be seen that the combination of the small holes andthe auxiliary chamber causes an increase in volume of the voice waveswhich it is desired to transmit and eliminates to a large extent theundesirable high frequency vibrations.

What is claimed is:

l. A telephone transmitter comprising a diaphragm, a plurality ofchambers resonant at voice frequencies located in serial re lation infront of said diaphragm and con-' stricted openings connecting saidresonating chambers.

2. A telephone transmitter comprisinga plurality of resonating chambers,one of said resonating chambers being resonant to any desired band ofvibrations within the voice frequency range for intensifying vibrationsof a predetermined frequency within said range, and means for shieldingeach of said chambers from vibrations having a frequency outside of therange of vibrations it is desired to transmit.

3. A telephone transmitter comprisin a diaphragm responsive tovibrations, an a plurality of chambers resonant at voice frequencies infront of said diaphragm, said chambers being of decreasing diameteroutwardly.

i. A telephone transmitter comprisin a diaphram, a thin resonatingchamber a jacent the diaphragm, an auxiliary chamber" resonant tofrequencies corresponding to voice vibrations, and a plurality ofrestricted openings connecting said chambers.

5. A telephone transmitter com rising a diaphragm, a face plate spaced ajacent to said diaphragm but separated therefrom to provide a thinchamber resonant at voice frequencies therebetween and an auxiliarychamber centrally located in the face plate, said face plate beingprovided with a plurality of small openings on either side of theauxiliary chamber.

6. A telephone transmitter comprising a diaphragm, a face plate adjacentthereto but separated therefrom to provide a thin resonating chamber, anair chamber resonant to vibrations within the range of voice frequenciescentrally located in said face plate, means for preventingvibrations offrequencies outside of the voice range from entering said auxiliarychamber, and means between said chambers for further filtering outvibrations outside of the range of voice frequencies.

7. A telephone transmitter comprising a diaphragm, a plurality ofchambers resonant at voice frequencies located in serial relation infront of said diaphragm, a plurality of sound filters separating saidresonating chambers.

In witness whereof, I hereunto subscribe my name this 3rd' day ofSeptember A. 1).,

JOHN P. MINTON.

